Microelectronic devices frequently include metal layers of platinum, gold, or such. The metal layers may be used in sensors, such as a thermistor, an ion sensitive field effect transistors (ISFET), and the like. Fabrication of the microelectronic devices frequently requires etching through an overlying dielectric layer containing silicon dioxide, silicon nitride, or such, to expose the metal layer. Etching silicon dioxide and silicon nitride, and subsequently stopping on the metal layer is challenging. Wet etch processes lack lateral dimensional control due to undercutting of the etch mask. Dry etching, such as reactive ion etching (RIE), tends to remove a portion of the metal layer and redeposit the metal on sidewalls of the overlying dielectric layer and etch mask, complicating removal of the etch mask and possibly contaminating the etch equipment. Moreover, adhesion of the dielectric layer to metals such as platinum and gold is often unreliable.